Ceramic instrument

ABSTRACT

The present invention relates to a rotating instrument made of a ceramic material and comprising a shaft  1  and a working member  2  which is secured to the shaft or can detachably be secured thereto, wherein at least part of the working member  2  is made from a ceramic material, characterized in that the ceramic part of the working member  2  has a surface roughness of 0.5 μm to 6 μm.

The present invention relates to a rotating instrument according to thepreamble of the main claim.

In detail, the present invention relates to a rotating instrumentcomprising a shaft and a working member which is secured to the shaft orcan detachably be secured thereto.

The prior art shows rotating instruments, e.g. dental instruments,drills, surgical saw blades, or the like, which are made from metallicmaterials. Depending on the respective field of application and theconfiguration of the rotating instrument, it may turn out to bedisadvantageous that metallic wear residues occur in the microrange andare disadvantageous during care or in the later healing process.

The known instruments are e.g. used in the dental field duringgeneration of bone cavities, during treatment of bones or, quitegenerally, during insertion of implants.

JP 05309102 A shows a dental instrument with a metallic shaft and aceramic working member. The ceramic working member is here covered withdiamond particles which form the cutting edges needed for treatment.

It is the object of the present invention to provide a rotatinginstrument of the above-mentioned type which while being of a simpleconstruction and producible in an easy and inexpensive way avoids thedrawbacks of the prior art and, in particular, has no objectionableinfluence on the metallic materials.

According to the invention this object is achieved by the features ofthe main claim; the subclaims show further advantageous designs of theinvention.

According to the invention it is thus intended that at least part of theworking member of the instrument is made from a ceramic material and hasa surface roughness of 0.5 μm to 6 μm. Preferably, the surface roughnessmay be in the range of 1 μm to 2 μm.

The rotating instrument according to the invention is characterized by anumber of considerable advantages. Due to the manufacture of the workingmember or at least a part thereof from a ceramic material, no problemswill arise with respect to metallic wear or metallic residues.Furthermore, any influence on the patient due to direct metallic contactcan be excluded.

A further advantage is e.g. also achieved in the case of ceramic veneersin the dental field. Any optical impairment, as is e.g. found inmetallic tools or instruments as a dark coloration, does also not arisebecause metallic wear is prevented. This yields a much better opticaloverall effect that decisively improves the subsequent treatment orsubsequent working steps.

The surface roughness provided according to the invention considerablyincreases the strength in the case of very small dimensions of dentalinstruments or surgical instruments. In particular, the occurrence ofmicrocracks, which would lead to breakage and thus to failure of theinstrument, is reliably prevented. The rotating instruments of theinvention are characterized by a maximum degree of strength despitetheir small dimensions and their small diameter.

A further measure for increasing the stability and for reducing notcheffects consists according to the invention in that all geometricallycreated form transitions of the ceramic part of the working member haveat least radii of 0.01 mm to 5 mm. Preferably, the radii are such thatthey do not fall below 0.5 mm. This avoids all sharp-edged transitions,e.g. in the case of changes in diameter, during provision of chipflutes, or the like. The indicated radii may also refer to the blank(green compact) of the instruments of the invention, from which thefinished instrument is then sintered or burnt. It will be understood bythose with ordinary skill in the art that the reference to geometricallycreated form transitions refers to any line on the ceramic part formedby the intersection of two surfaces at an angle of other than 180°.

A further measure for enhancing the stability of the inventiveinstruments, which are operated at very high speeds as is e.g. standardin dental drills or the like, consists in providing a core reinforcementwhich comprises that part of the ceramic portion of the working memberthat the underlies and is not penetrated by the grooves or cuts in theceramic portion of the working member. Thus, for example, in FIG. 6, theportion of the ceramic portion of the working member that is shown incross-section as lying inwardly of the cutting edges or teeth of theceramic portion of the working member comprises the core reinforcementof the ceramic portion of the working member. This can be created byreducing the depth of grooves or cuts from the free end of the workingmember to the opposite area of the working member adjoining the shaft.The core reinforcement in that case forms an imaginary conical basicshape that may for example increase at an angle of 0.25° to 3° towardsthe shaft. A preferred value is in the range of 1°. The conicalconfiguration and the related tapering of the ceramic portion of theworking member are shown in FIGS. 4 and 5 of the drawings.

To avoid the occurrence of microcracks, or the like, a microhardening ofthe structure of the surface of the ceramic part of the working memberis intended. The bending strength of the instruments according to theinvention can considerably be increased thereby. The microhardeningprocess can be carried out by blasting the surface (by using particles).As will be understood by those of ordinary skill in the art, themicrohardness of a surface is a measure of the hardness of the surfaceas determined by a Vickers or Knoop tester as set forth, for example, inASTM E-384 and the microhardening of a surface increases the hardness,as measured by a Vickers or Knoop tester. Additionally, increasing themicrohardness of the surface of the ceramic portion of the workingmember will increase its bending strength.

It may be of advantage for protection against wear or for improving thefriction properties to provide the surface of the ceramic part of theworking member with a hard layer. This layer may e.g. be a TiN layer ora DLC layer.

The use of the ceramic instrument according to the invention is improvedby a depth mark. This can be carried out by cut-in grooves which arerounded in the groove bottom (as mentioned above) or by applying alaser. During marking by means of a laser a complete blackening of thearea of the ceramic surface to be marked is possible. Alternatively, itis also possible to apply a structure or a geometrical shape which neednot be given a surrounding configuration and only creates the impressionof a continuous blackening during rotation of the instrument.

The depth mark may e.g. have a surface roughness in the range of 1 μm to10 μm, a preferred range being 2 μm to 4 μm.

According to the invention it is possible to make the working member andthe shaft from the ceramic material. It is possible to join individualceramic components or also to form the rotating instrument in one piece.

A further advantageous configuration of the invention is that theworking member comprises a metallic carrier and at least one layer thatis applied thereto and consists of the ceramic workpiece. Instead of thelayer, it is also possible to provide an additional ceramic component.The connection may e.g. be established with the help of an adhesive,e.g. by means of a temperature-stable composite.

To make the surface of the ceramic material without pores and to make itsmooth, it is advantageous when the surface is ground or polished.

According to the invention it is possible to provide the ceramicmaterial with cutting edges and/or a toothing. It is e.g. possible toconfigure the instrument of the invention as a saw blade to carry outbone cuts, or the like.

On the whole, the rotating instrument of the invention may be designedas a dental instrument, e.g. as a bone drill or the like. However, it isalso possible to design said instrument as a pure grinding or separatingtool, e.g. also as a saw blade.

It has turned out to be particularly advantageous when an aluminum oxideand/or a zirconium oxide is/are used as the ceramic material. Mixturesof said two oxides may also be of advantage (e.g. Al₂O₃ or ZrO₂). Such amixed ceramic material has excellent properties with respect to thebending strength and toughness. A further variant consists in usingzirconium oxide with tetragonal zirconium polycrystals. Such a ceramicmaterial has an even finer grain and thus improved mechanicalproperties, particularly an increased breaking strength. An improvedresistance to aging is accomplished with a corresponding Al₂O₃ doping.Such a material shows an excellent biocompatibility.

The instruments of the invention may also be provided with an internalcooling. A continuous drilled hole may e.g. serve this purpose, whichhole preferably comprises a plurality of exit openings in the area ofthe working member of the instrument.

The instrument according to the invention may e.g. be provided with twoto three cutting edges, but it is also possible to provide only onecutting edge or a greater number of cutting edges, e.g. four to tencutting edges.

The toothing (pattern) or grinding of the cutting edges may also bevaried. For instance, it is possible to provide a double toothing orcross toothing or a total of three toothings or grindings.

The instrument of the invention may be designed as a drilling or millinginstrument; the working member may be configured to be spherical,cylindrical, cylindrical-round, conical, conical-round, stepped or as athread cutter.

The present invention will now be explained with reference toembodiments taken in conjunction with the drawing, in which:

FIG. 1 is a side view, partly in section, of a first embodiment of aninstrument according to the invention in the form of a dental drill;

FIG. 2 is a side view of a further embodiment of a dental instrumentaccording to the invention, said instrument being configured in the formof a crown separator;

FIG. 3 is a side view of a further embodiment of an instrument accordingto the invention, said instrument being configured as an implantologypilot drill;

FIG. 4 is a simplified side view of a further embodiment of aninstrument according to the invention in the form of a bone cutter;

FIG. 5 is a side view of the instrument shown in FIG. 4, in anillustration turned by 90°;

FIG. 6 is a sectional view taken along line A-A of FIG. 5;

FIG. 7 is a side view of an instrument formed as an implantology pilotdrill;

FIG. 8 is a front view of the instrument shown in FIG. 7; and

FIG. 9 shows details Z of FIG. 7.

The rotating instrument of the invention as shown in FIG. 1 isconfigured in the form of a drill. Said drill comprises a shaft 1 havingan axis of rotation and a working member 2 which, as is customary with adrill, is provided with cutting edges. The working member 2 need not beillustrated or described in detail because such drills are already knownfrom the prior art.

According to the invention a bolt-like or mandrel-like carrier 3 issecured to the shaft 1 or integrally connected to the shaft 1. Thecarrier 3 is arranged in a central recess of the working member 2 andthus surrounded by a layer 4 of a ceramic material.

As shown by the detail views of FIG. 1, the carrier 3 may e.g. have ahexagonal cross-section. It may also be provided with a roundcross-section which is e.g. equipped with grooves or a thread.

The shaft 1 and the carrier 3 may be made from steel, e.g. from RFsteel.

FIGS. 2 and 3 show further embodiments of the rotating instruments ofthe invention, wherein the working member 2 is each time made from aceramic material or provided with a layer of a ceramic material. Theinstrument shown in FIG. 2 is configured in the form of a crownseparator whereas the instrument shown in FIG. 3 represents animplantology pilot drill.

FIGS. 4 to 6 show an embodiment in which the instrument of the inventionis configured in the form of a bone cutter. The working member 2 may bemade integral with the shaft.

Furthermore, the working member 2 comprises crossing cuts or toothings,as shown in FIGS. 4 and 5. The tip of the bone cutter shown in FIGS. 4and 5 has a clearance cut 10 which may e.g. be 10°. Reference numeral 11designates a tip angle which may e.g. be 100°. The diameter in the areaof the tip may e.g. be 1.44 mm while the length of the working member 2is 10 mm. The total length of the instrument is e.g. 44.5 mm.

The further dimensions of the instrument may be as follows:

-   Working partial length: 1-25 mm-   Working partial diameter: 1-25 mm-   Tip clearance cut: 0-40°-   Tip angle: 50-150°-   Clearance angle: 0°-70°-   Cutting angle: −10°-20°-   Twist: 0-80°-   Number of teeth: 1-20

A cross toothing with a twist of 20° to 70° is also possible. Likewise,a transverse cut for optimizing the cutting behavior with a pitch of 0.5of 2.0 mm is also advantageous in a preferred development.

FIG. 6 shows the possible angle once again. It shows, for instance, aclearance angle 12 of 35°. A cutting angle 13 may e.g. be 0° (for betterillustration the cutting angle 13 is drawn on an exaggerated scale). Awedge angle 14 is e.g. 50°.

FIGS. 7 to 9 show a further embodiment in which the instrument isconfigured in the form of an implantology pilot drill. This drill maye.g. have the following dimensions:

-   Working partial length: 1-25 mm-   Working partial diameter: 1-8 mm-   Tip clearance cut: 0-40°-   Tip angle: 50-150°-   Clearance angle: 0-60°-   Cutting angle: 0-20°-   Twist: 0-60°-   Number of teeth: 1-10

FIG. 8 shows, for instance, a cutting angle 13 of 10° and a clearanceangle 12 of 8°. Reference numeral 15 designates a clearance cut of thecutting edge which is e.g. 12° whereas reference numeral 16 shows aclearance cut of the cutting edge of 25°.

The implantology pilot drill shown in FIGS. 7 to 9 may be provided withone or several depth marks 17. As shown in FIG. 9, these may havedifferent optical shapes. Detail Z1 shows a complete blackening, detailZ2 an inclined line mark, detail Z3 a cross mark whereas each of detailsZ4 and Z5 comprises parallel lines. Detail Z6 shows a variant with apoint pattern.

The above-described ceramic materials used according to the inventionmay have the following values:

As illustrated in the various figures of the drawings, the workingmember (2) of each embodiment is characterized in that the outer surfaceof the working member is configured, such as for example by theinclusion of flutes, to allow material cut away by the at least onecutting edge and/or toothing to proceed along the outer surface of theworking member (2) in a direction that extends generally along the axisof rotation of the shaft (1).

-   Hardness: 1200-1500-   Density: 5.4-6.1-   Bending strength: 1200-3000

As indicated above, a means of increasing the stability and reducingnotch effects involves providing radii of 0.01 mm to 5 mm, andpreferably not less than 0.5 mm, at all geometrically created formtransitions of the ceramic part of the working member so as to avoid allsharp-edge transitions such as changes in diameter during the provisionof chip flutes or the like. The reference to geometrically created formtransitions refers to any line on the ceramic part, other than a cuttingedge, that is formed by the intersection of two surfaces at an angle ofother than 180°. The foregoing radii may also be applied to the blank(green compact) of the instruments of the invention from which thefinished instrument is then sintered or burnt.

Also as indicated above, a further measure for enhancing the stabilityof the instruments of the invention comprises providing a corereinforcement, the core of the instrument comprising that part of theceramic portion of the working member that underlies and is notpenetrated by the grooves or cuts in the ceramic portion of the workingmember. The core reinforcement is created by reducing the depth ofgrooves or cuts from the free end of the working member to the oppositeend of the working member adjacent the shaft of the working member. Thecore reinforcement may increase at an angle of 0.25° to 3°, preferablyin the range of 1°, toward the shaft from the free end of the workingmember.

The occurrence of microcracks and the like can be avoided bymicrohardening the structure of the surface of the ceramic portion ofthe working member. The bending strength of the instruments of theinvention can be increased as a result. The microhardening process canbe carried out by blasting the surface of the ceramic portion of theworking member using particles for example. As will be understood bythose of ordinary skill in the art, the microhardness of a surface is ameasure of the hardness of the surface as determined by a Vickers orKnoop tester as set forth, for example, in ASTM E-384. And themicrohardening of a surface increases the hardness of the surface asmeasured by a Vickers or Knoop tester. Also, increasing themicrohardness of the surface of the ceramic portion of the workingmember can increase its bending strength.

The invention is not limited to the illustrated embodiments. Rather,many alterations and modifications are possible within the scope of theinvention.

LIST OF REFERENCE NUMERALS

-   1 shaft-   2 working member-   3 carrier-   4 layer-   10 clearance cut-   11 tip angle-   12 clearance angle-   13 cutting angle-   14 wedge angle-   15 clearance cut-   16 clearance cut-   17 depth mark

1. A dental instrument comprising: a shaft (1); and a working member (2)which is secured to the shaft, said dental instrument having alongitudinal axis of rotation, said dental instrument being sized andconfigured to perform a dental procedure in a person's mouth, saiddental instrument being sized and configured to rotate at a high speedeffective to perform said dental procedure, wherein at least part of theworking member (2) is made from a ceramic material, characterized inthat at least one cutting edge and/or toothing consisting of the ceramicmaterial is provided in the outer surface of the at least part of theworking member (2) that is made from the ceramic material such that theat least one cutting edge and/or toothing consisting of the ceramicmaterial is adapted to perform a cutting function during the dentalprocedure, wherein the at least part of the working member (2) made fromthe ceramic material and containing the at least one cutting edge and/ortoothing consisting of the ceramic material has a surface roughness of0.5 μm to 6 μm.
 2. The instrument according to claim 1, characterized inthat the at least part of the working member (2) made from the ceramicmaterial has a surface roughness of 1 μm to 2 μm.
 3. The instrumentaccording to claim 1, characterized in that all geometrically createdform transitions of the at least part of the working member (2) madefrom the ceramic material have radii of at least 0.01 mm to 5 mm.
 4. Theinstrument according to claim 1, characterized in that all geometricallycreated form transitions of the at least part of the working member (2)made from the ceramic material have radii of at least 0.5 mm.
 5. Theinstrument according to claim 1, characterized in that the workingmember (2) is provided with a core reinforcement defined by the depth ofgrooves or cuts made to provide the at least one cutting edge and/ortoothing and the depth of the grooves or cuts is reduced from the freeend to the shaft of the working member (2).
 6. The instrument accordingto claim 5, characterized in that the core reinforcement has asubstantially conical basic shape.
 7. The instrument according to claim5, characterized in that the core diameter increases by 0.25° to 3°towards the shaft.
 8. The instrument according to claim 5, characterizedin that the core diameter increases by 1° towards the shaft.
 9. Theinstrument according to claim 1, characterized in that the at least partof the working member (2) made from the ceramic material has amicrohardened surface.
 10. The instrument according to claim 1,characterized in that the surface of the at least part of the workingmember (2) made from the ceramic material is provided with a hard layer.11. The instrument according to claim 1, characterized in that thesurface of the at least part of the working member (2) made from theceramic material has a depth mark.
 12. The instrument according to claim11, characterized in that the depth mark has a surface roughness of 1 μmto 10 μm.
 13. The instrument according to claim 11, characterized inthat the depth mark has a surface roughness of 2 μm to 4 μm.
 14. Theinstrument according to claim 11, characterized in that the depth markis a laser mark.
 15. The instrument according to claim 11, characterizedin that the depth mark comprises cut-in grooves.
 16. The instrumentaccording to claim 1, characterized in that the entire working member(2) and the entire shaft (1) are made from a ceramic material.
 17. Theinstrument according to claim 1, characterized in that the workingmember (2) has a metallic carrier (3) and at least one layer (4) that isprovided thereon and comprises the at least one part of the workingmember (2) that is made of the ceramic material.
 18. The instrumentaccording to claim 17, characterized in that the layer (4) of theceramic material is connected to the carrier (3) by means of anadhesive.
 19. The instrument according to claim 1, characterized in thatthe at least part of the working member (2) that is made from theceramic material has a surface that is free of pores.
 20. The instrumentaccording to claim 1, characterized in that the ceramic materialcomprises aluminum oxide and/or zirconium oxide.
 21. The instrumentaccording to claim 1, characterized in that said instrument is a drill.22. The dental instrument according to claim 1, wherein said workingmember has a length of 1-25 mm and a diameter of 1-25 mm.
 23. The dentalinstrument according to claim 1, wherein said working member has adiameter of 1-8 mm.
 24. The dental instrument according to claim 1,wherein said ceramic material has a density of 5.4 to 6.1 g/cm³.
 25. Thedental instrument according to claim 1, wherein said working member hasa twisted groove for material cut away.
 26. The dental instrumentaccording to claim 1, wherein said working member is detachably securedto the shaft.
 27. A method of performing a dental procedure comprisingthe steps of: (a) providing a dental instrument, said dental instrumentcomprising a shaft and a working member which is secured to the shaft,said dental instrument having a longitudinal axis of rotation, saiddental instrument being sized and configured to perform the dentalprocedure in a person's mouth, said dental instrument being sized andconfigured to rotate at a high speed effective to perform the dentalprocedure, wherein at least part of the working member is made from aceramic material, characterized in that at least one cutting edge and/ortoothing consisting of the ceramic material is provided in the outersurface of the at least part of the working member that is made from theceramic material such that the at least one cutting edge and/or toothingconsisting of the ceramic material is adapted to perform a cuttingfunction during the dental procedure, wherein the at least part of theworking member made from the ceramic material and containing the atleast one cutting edge and/or toothing consisting of the ceramicmaterial has a surface roughness of 0.5 μm to 6 μm; (b) rotating saiddental instrument about said longitudinal axis of rotation; and (c)causing said rotating dental instrument to contact tooth or bone and cutsaid tooth or bone in the course of the dental procedure.
 28. The methodof claim 27 characterized in that all geometrically created formtransitions of the at least part of the working member made from theceramic material have radii of at least 0.01 mm to 5 mm.
 29. The methodof claim 27, characterized in that the at least part of the workingmember made from the ceramic material is provided with a corereinforcement defined by the depth of grooves or cuts made to providethe at least one cutting edge and/or toothing and the depth of thegrooves or cuts is reduced from the free end to the shaft of the workingmember.
 30. The method of claim 27, characterized in that the surface ofthe at least part of the working member made of the ceramic material ismicrohardened.
 31. The method of claim 27, characterized in that thesurface of the at least part of the working member made from the ceramicmaterial is provided with a hard layer.
 32. The method of claim 27,characterized in that the surface of the at least part of the workingmember made from the ceramic material has a depth mark.
 33. The methodof claim 27, characterized in that the dental procedure is selected fromthe group consisting of the generation of bone cavities, the treatmentof bones and the insertion of implants.